The invention relates to a coupling device for a pipe, comprising a sleeve having an insert end for the pipe and a sealing means adapted for realizing a seal around the pipe when inserted in the sleeve, said sealing means comprising a plurality of mutually slidable elements which together form a ring, and a grip ring being mounted within said elements and extending along at least a part of the perimeter of the pipe.
Such a coupling device is disclosed in the European patent application EP-A-0 794 378, to which U.S. application Ser. No. 08/790,196 corresponds, which has been incorporated by reference, and assigned to the present applicant""s assignee. The coupling device may be used for pipes made of steel, stainless steel, etemite, cast-iron, coated steel, PVC, polyethylene and asbestos cement, and may be used to couple two of such pipes. It is important that on the one hand the coupling device provides a sufficient seal, and that on the other hand the coupling device is able to withstand tensile strain. The latter function is provided by the grip ring which is part of the prior art coupling device.
It is the objective of the invention to improve the function of said grip ring. Said objective is achieved by the inventive coupling device being characterized in that the grip ring is provided with dents pressed out of the plane of the grip ring.
It is particularly desirable that the dents which are pressed out of the plane of the grip ring are adjacent to slit-like openings punched out of the grip ring. It has been shown that the resistance to tensile strain of the coupling device according to the invention is thereby considerably improved with respect to the coupling device of EP-A-0 794 378. Employment of such a coupling device with hard pipes like pipes of cast-iron, steel, stainless steel and the like, having a diameter of 150 mm results in the prior art in an achievable resistance to tensile strain of 7 bar. Said value amounts to 40 bar when employing the inventive coupling device. According to the inventor this is brought about by the burr which results when punching the openings out of the plane of the grip ring.
It is preferred that the openings have a width B such that the ratio B/D is less than 3, D being the thickness of the grip ring. In this way the grip ring which is part of the coupling device according to the invention remains sufficiently strong in spite of the formation of the openings.
It is preferred that the dents approximately halfway the openings are situated maximally out of the plane of the grip ring. In this way approximately triangle-like dents are provided, burrs formed by punching of the openings and located at the edge of said dents being optimally effective in providing grip on the pipes with which the coupling device is employed.
It is further preferred that the grip ring is made of stainless spring steel having a tensile strength of at least 1200 N/mm2, preferably approximately 1400-1600 N/mm2. In this way the effectiveness of the grip provided according to the invention may be maximally employed because the strength characteristics inherent to such material are fully utilized by cold deformation of the material due to punching and dent-formation which increases the tensile strength.
The invention is also embodied in a method for fabricating a grip ring to be used in a coupling device according to the invention, said method being characterized in that the slit-like openings are punched and that subsequently in a forming process small dents are pressed out of the plane of the plate adjacent to the openings, followed by giving the plate an at least approximately ring-shape.